Semiconductors are widely used in integrated circuits for electronic applications, including radios, computers, televisions, and high definition televisions. Such integrated circuits typically use multiple transistors fabricated in single crystal silicon. Many integrated circuits now contain multiple levels of metallization for interconnections.
Aluminum-copper (AlCu) alloys are typically used in VLSI (very large scale integration) metallization. To enhance the speed of devices, a low and stable sheet resistance is required for AlCu. However, AlCu can react with other metals (e.g. W) thereby increasing its sheet resistance. Sheet resistance is a measurement of a conductive material with a magnitude proportional to resistivity and inverse of thickness. TiN has been applied as a diffusion barrier between AlCu and the other metals to suppress their reactions. However, heat treatment of AlCu/TiN layered structures at 450.degree. C. induces reactions between the AlCu and TiN, leading to an increase in the sheet resistance of the AlCu.
Several attempts have been made to improve the barrier properties of TiN in Al/TiN/Si, Al/TiN/silicide/Si and Al/TiN/W structures. In the past, the improvement of TiN barriers have mostly been achieved by optimizing the parameters during TiN deposition, such as introducing oxygen flow during deposition, changing the substrate temperature, or adding a substrate voltage bias. Other attempts have included post-deposition treatments such as thermal annealing and exposure to air.